Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack,a mechanical performance design method of cement sheath i...Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack,a mechanical performance design method of cement sheath is established to meet the wellbore sealing requirements during fracturing.This method takes the failure types of the cement sheath,such as tensile failure,plastic yield,interface crack propagation along interface and zigzag propagation into account.Meanwhile,the elasticity modulus and Poisson's ratio quantitative design charts of cement sheath are constructed based on this method,and the safety and risk areas of wellbores are defined,which quantify the yield strength and tensile strength indexes of cement sheath.The results show that decreasing elasticity modulus,increasing yield strength and Poisson's ratio of cement sheath can avoid plastic deformation of cement sheath;increasing the tensile strength of cement sheath can prevent its tensile failure;increasing elasticity modulus and Poisson's ratio of cement sheath is good for shortening the length of the interface crack,but will increase the risk of interface cracks zigzagging into cement sheath.The model calculation and case verification has proved that the method in this paper can give accurate calculation results and is convenient for field application.展开更多
基金Supported by Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(2020CX040000)Sichuan Science and Technology Program(2020JDTD0019)+1 种基金National Natural Science Foundation of China(52004231)Research Project of Dagang Oilfield(NO.DGYT-2018-JS-244).
文摘Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack,a mechanical performance design method of cement sheath is established to meet the wellbore sealing requirements during fracturing.This method takes the failure types of the cement sheath,such as tensile failure,plastic yield,interface crack propagation along interface and zigzag propagation into account.Meanwhile,the elasticity modulus and Poisson's ratio quantitative design charts of cement sheath are constructed based on this method,and the safety and risk areas of wellbores are defined,which quantify the yield strength and tensile strength indexes of cement sheath.The results show that decreasing elasticity modulus,increasing yield strength and Poisson's ratio of cement sheath can avoid plastic deformation of cement sheath;increasing the tensile strength of cement sheath can prevent its tensile failure;increasing elasticity modulus and Poisson's ratio of cement sheath is good for shortening the length of the interface crack,but will increase the risk of interface cracks zigzagging into cement sheath.The model calculation and case verification has proved that the method in this paper can give accurate calculation results and is convenient for field application.
